This report describes an application of Clustering and Differential Geometry to the characterization of digital terrain maps by different surface types and critical regions. Of particular interest is the determination of specific terrain types, where they occur, and describing them in ways which are invariant to viewing position. The development of robust and efficient segmentation and associated region characterization procedures is reported. Good results have been obtained for characterizing digital terrain maps. This work supports the development of techniques for generating optimal flight paths.